Recently, Orthogonal Frequency Division Multiplexing (OFDM) is becoming very popular for modern broadband wireless communication systems and the 3rd Generation Long Term Evolution (3GPP LTE) has adopted OFDM. LTE defines a Physical Downlink Control Channel (PDCCH), which conveys UE-specific control information including downlink resource allocation, uplink resource allocation, and broadcast control channel. LTE Advanced (LTE-A) is a major enhancement of 3GPP LTE to meet target data rates of 1 Gbits for high mobility and 100 Mbits low mobility with very high spectrum allocation of 100 MHz by aggregating multiple 20 MHz LTE bands. With the increase of system bandwidth, it is plotted to evolve to 5 LTE-A systems while maintaining use of 20 MHz LTE bands.
The downlink resource allocations of the conventional LTE and LTE-A are described with reference to FIGS. 1 and 2.
An LTE-A system can be implemented by aggregating 4 LTE systems using the LTE bands. Referring to FIG. 1, in the LTE system using the first frequency band f1, a sub-frame is composed of 14 OFDM symbols of which up to three can be used for control channels. In FIG. 1, three OFDM symbols are used for the control channels exemplarily. Here, a Physical Downlink Control Channel (PDCCH) can be encoded at different coding rates (CRs) depending on the channel condition and transmitted on 1, 2, 4, or 8 Control Channel Elements (CCEs), where a CCE corresponds to 9 Resource Element Groups (REGs) and an REG corresponds to 4 OFDM subcarriers. FIG. 1 shows an exemplary case in which the PDCCH is transmitted on two CCEs for allocating downlink resource. A base station informs a user equipment of the downlink resource with the resource allocation information within the PDCCH. In case of LTE-A system, the base station allocates downlink resources to the UE for the respective frequency bands (i.e. f1, f2, f3, and f4) using individual PDCCHs. For instance, the PDCCH of f1 is used for allocating traffic channel resource for f1, and the PDCCH of f2 is used for allocating traffic channel resource for f2. The LTE-A system depicted in FIG. 1 is implemented for use of wider frequency band while reusing all the functionalities of LTE system. Here, the downlink resource allocation by transmitting the PDCCH on two 2 CCEs is depicted as an example, but in can be applied for uplink resource allocation and resource allocation using a MIMO function.
FIG. 2 shows an exemplary downlink resource allocation technique in which the downlink resources for the entire system frequency band including f1, f2, f3, and f4 are allocated using a single PDCCH in frequency band f4. In the system of FIG. 2, a PDCCH of a frequency band includes additional information on the other bands for the UE to discriminate the downlink resources allocated in different frequency bands.
Although it is advantageous to allocate the resources of frequency bands of different LTE systems using a single frequency band, the conventional resource allocation method has a drawback in that the information amount increases due to the additional information for discriminating the frequency bands.